If we choose to live near convergent plate boundaries, we can build buildings that can resist earthquakes, and we can evacuate areas around volcanoes when they threaten to erupt. Yes, convergent boundaries are dangerous places to live, but with preparation and watchfulness, the danger can be lessened somewhat.
Nitrification, as stated above, is formally a two-step process; in the first step ammonia is oxidized to nitrite, and in the second step nitrite is oxidized to nitrate. Different microbes are responsible for each step in the marine environment.
The human body is exposed. to nitrates and nitrite every day from a wide variety of sources, including production by our own systems. Children over six months of age, older children and adults have sufficient internal mechanisms to remove. nitrate and nitrite from the body.